The invention relates to the field of medical engineering, and more particularly to micromechanics and medical measuring technology.
Modern medicine employs microinvasive techniques in a variety of ways and to an increasing degree, so as to achieve maximum supportive, therapeutic or diagnostic success with minimal impact on the patient.
Examples of such techniques include the insertion of stents in blood vessels, the use of thrombus filters, the removal of deposits in blood vessels by milling, and the support or temporary or partial replacement of a patient's cardiac function through micropumps/blood pumps that are introduced in blood vessels.
Many of these techniques require appropriate functional elements to be introduced via the bloodstream into the patient's body by means of a catheter and to be positioned within the bloodstream in the most expedient manner possible.
Precise position control to as great an extent as possible is not only desirable, initially or during acute use, for example on a milling head, as well as in the long term, but also decisive for the success of the invasive measure.
Positioning plays a critical role especially with blood pumps because these often remain in the patient's body for extended periods and must operate reliably without constant supervision by medical staff, wherein in the case of a catheter configuration, notably with access via a femoral artery, the risk of shifting exists due to active or passive body movements. The precision with which blood pumps are placed is also subject to stringent requirements, especially when these are located in the vicinity of a heart valve or cooperate with a heart valve.
Often times the positions of the corresponding functional elements are analyzed using radioscopy or by means of transesophageal echocardiography. However, these methods are tied to complex devices, which are not always available. This makes the position determination not only complex and expensive, but in many instances it is also not practical or useful given the extreme time pressure. While in emergencies, it is possible to place an intra-aortic pump blindly by measuring the distance between the puncture site in the groin and the jugular notch. However, this presupposes normal anatomic circumstances and carries with it the risk of misplacement in the contralateral femoral artery. This method is also imprecise because the individual anatomic features of the aorta are not predictable. If the functional element, in particular the pump, cannot be optimally placed, the supporting effect of such a pump is not optimal, and other functional elements can likewise not function optimally.
In addition to the pure transillumination method, other options are known from the prior art for determining the position of a component, and more particularly that of a cardiac catheter, substantially precisely.
U.S. Pat. No. 5,983,126, for example, discloses the application of three orthogonal external signals outside the patient body to the positioning area, wherein a probe is used to measure the influence of the three signals on the functional element and thus conclude the position. The corresponding external signals must be designed so that they do not interfere with the electrophysiological signals of the heart.
U.S. Pat. No. 6,226,546 B1 describes a catheter localization method using a plurality of acoustic probes at the catheter head, wherein signals emitted by the probes are received via acoustic receivers and processed by a processing unit so as to determine the position and map the anatomic environment of the probes.
A catheter localization method having an accuracy of approximately 1 mm is known from U.S. Pat. No. 5,391,199, in which a transmitter outside the patient body emits signals by means of an antenna and receiving antennas are provided at the catheter tip, which are connected to a receiver for processing the signals. The signals are compared to corresponding reference signals from reference antennas in the patient's body.
Devices and methods for recording and mapping the electrophysiological activity inside a heart by means of a cardiac catheter are known from U.S. Pat. No. 6,892,091 B1. The corresponding catheter also comprises a position sensor, which is designed as an electromagnetic sensor. The exemplary embodiment regarding the use of such a position sensor described involves the application of magnetic fields which are generated outside the patient body and which act on the position sensor, so that both a position and an orientation of the sensor, and thus of the catheter, can be determined by means of the sensor. In addition, the comparison to reference signals of additionally introduced catheters is described.
The methods known from the prior art all have complex equipment in common, either in form of imaging devices or of additional signal sources outside the patient body. Such methods are not suitable for everyday use that is otherwise unproblematic, with a blood pump that is operated for cardiac support purposes for extended periods without the supervision of medical staff.